<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <script src="js/jquery-3.3.1.js"></script>
    <script type="application/javascript">
        $(function () {
            //1: 给用户名输入框绑定失去焦点事件(onfocus  onblur)
            $("#username").on("blur",function () {
                //获取用户名输入框数据
                var username =  $("#username").val();
                //2:向服务器发出异步请求，让服务器去查询用户名是否存在
                $.post(
                    "register", //表示服务器的servlet路径
                    "username="+username,  //表示向服务器发送的数据
                    function (data) {  // msg:用户名已经注册  code:0
                        if(data.code==0){
                            // alert(data.info);
                            $("#spanId").html(data.msg).css("color","green");
                        }else {
                            $("#spanId").html(data.msg).css("color","red");
                        }

                    },
                    "json"
                );
            });
        });

    </script>
</head>
<body>
<div>
    <font>会员注册</font>USER REGISTER
    <form class="form-horizontal" style="margin-top: 5px;">
        <table>
            <tr>
                <td>用户名</td>
                <td>
                    <input type="text" id="username" name="username" placeholder="请输入用户名">
                    <span id="spanId"></span>
                </td>
            </tr>
            <tr>
                <td>密码</td>
                <td>
                    <input type="password" placeholder="请输入密码">
                </td>
            </tr>
        </table>
        <input type="submit" value="注册"/>
    </form>
</div>

</body>
</html>